The present invention relates generally to x-ray detectors and, more particularly, to a method and system of detecting, measuring, and providing feedback as to gravitational loads placed on an x-ray detector.
X-ray imaging is a non-invasive technique to capture images of medical patients for clinical diagnosis as well as inspect the contents of sealed containers, such as luggage, packages, and other parcels. To capture these images, an x-ray source irradiates a scan subject with a fan beam of x-rays. The x-rays are then attenuated as they pass through the scan subject. The degree of attenuation varies across the scan subject as a result of variances in the internal composition of the subject. The attenuated energy impinges upon an x-ray detector designed to convert the attenuating energy to a form usable in image reconstruction. A control system reads out electrical charge stored in the x-ray detector and generates a corresponding image. For a conventional, screen film detector, the image is developed on a film and displayed using a backlight.
Increasingly, flat panel, digital x-ray detectors are being used to acquire data for image reconstruction. Flat panel detectors are generally constructed as having a scintillator which is used to convert x-rays to visible light that can be detected by a photosensitive layer. The photosensitive layer includes an array of photosensitive or detector elements that each store electrical charge in proportion to the light that is individually detected. Generally, each detector element has a light sensitive region and a region comprised of electronics to control the storage and output of electrical charge. The light sensitive region is typically composed of a photoconductor, and electrons are released in the photoconductor when exposed to visible light. During this exposure, charge is collected in each detector element and is stored in a capacitive element (diode) situated in the electronics region. After exposure, the charge in each detector element is read out using logic controlled electronics.
Each detector element is conventionally controlled using a transistor-based switch. In this regard, the source of the transistor is connected to the diode, the drain of the transistor is connected to a readout line, and the gate of the transistor is connected to a scan control interface disposed on the electronics in the detector. When negative voltage is applied to the gate, the switch is driven to an OFF state, i.e. no conduction between the source and drain. On the other hand, when a positive voltage is applied to the gate, the switch is turned ON resulting in connection of the source to the drain. Each detector element of the detector array is constructed with a respective transistor and is controlled in a manner consistent with that described below.
Specifically, during exposure to x-rays, negative voltage is applied to all gate lines resulting in all the transistor switches being driven to or placed in an OFF state. As a result, any charge accumulated during exposure is stored in each detector element capacitor. During read out, positive voltage is sequentially applied to each gate line, one gate at a time. In this regard, only one detector element is read out at a time. A multiplexer may also be used to support read out of the detector elements in a raster fashion. An advantage of sequentially reading out each detector element individually is that the charge from one detector element does not pass through any other detector elements. The output of each detector element is then input to a digitizer that digitizes the acquired signals for subsequent image reconstruction on a per pixel basis. Each pixel of the reconstructed image corresponds to a single detector element of the detector array.
As described above, indirect detection, digital x-ray detectors utilize a layer of scintillating material, such as Cesium iodide (Csl), to convert incident radiation to visible light that is detected by light sensitive regions of individual detector elements of a detector array. Generally, the transistor controlled detector elements are supported on a thin substrate of glass. The substrate, which supports the detector elements as well as the scintillator layer, is supported by a panel support. The support panel is not only designed to support the detector components, but also isolates the electronics for controlling the detector from the detector components. The electronics is supported by the base of a cover assembly enclosing the internal components of the x-ray detector.
The internal components of an x-ray detector, e.g. scintillator layer, detector array, glass substrate, etc., are relatively sensitive components that may fracture when subjected to relatively high levels of strain, stress, and acceleration. As such, when an x-ray detector is dropped, the internal components may be become damaged and degrade detector performance. As a result, the x-ray detector will require repair or replacement—two potentially costly solutions.
For instance, a user may not appreciate the degree to which an x-ray detector is dropped when the x-ray detector is, in fact dropped. In this regard, the user, such as a member of a hospital staff, may place the x-ray detector into use notwithstanding the damage caused to the x-ray detector as a result of the drop. Placing the x-ray detector can result in significant delay in acquiring usable data from a subject as the damage to the internal components of the x-ray detector will not be made apparent until data is acquired and reconstructed.
Since repair and replacement can be a time-consuming, arduous, and complex task, if a diagnostician diagnosing an inoperable or malfunctioning x-ray detector had specific insight as to whether the x-ray detector has been dropped, the diagnostic process may be expedited. That is, using empirical data, the diagnostician may be able to target the diagnostic process on the premise that given gravitational loads on the x-ray detector result in given damage to the x-ray detector and its components. For instance, if a diagnostician knew that the x-ray detector was subjected to a drop that placed a 10 g load on the x-ray detector, the diagnostician may able to discern that more than likely the glass substrate has fractured without disassembling the detector.
Therefore, it would be desirable to have an x-ray detector that detects and provides an output of the gravitational forces placed thereon whereby the output may be readout electronically such that diagnosis may be carried out without disassembly of the detector. It would be further desirable to have an x-ray detector that time and date stamps the gravitational loads placed thereon and stores this historical data in such a manner that it can be accessed to determine with specificity when the gravitational forces were placed on the detector.